Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$9.25	10.836%	$10.2523	$10.25	$10.25	$10.30
Purchase #2	$149.34	11.355%	$166.2976	$166.30	$166.30	$166.30
Purchase #3	$170.75	3.108%	$176.0569	$176.06	$176.05	$176.10
Purchase #4	$244.74	3.670%	$253.722	$253.72	$253.70	$253.70
Purchase #5	$72.92	8.197%	$78.8973	$78.90	$78.90	$78.90
Purchase #6	$177.71	3.866%	$184.5803	$184.58	$184.60	$184.60
Purchase #7	$249.33	12.476%	$280.4364	$280.44	$280.45	$280.40
7 purchase totals =	$1,074.04		$1,150.2428	$1,150.25	$1,150.25	$1,150.30